Efficient use of an implantable pulse generator battery, and associated systems and methods

ABSTRACT

Systems and methods for the efficient use of an implantable pulse generator (IPG) battery are disclosed. A representative system for adjusting an electrical signal of an IPG associated with delivering therapy to a patient comprises a computer readable medium having instructions that cause the IPG to deliver a supply voltage at a first value, adjust the supply voltage from the first value until a threshold break occurs, and, based at least in part of the threshold break, increase the supply voltage from the second value to a third value. As therapy is delivered to the patient, the system iteratively adjusts the supply voltage to approach and reflect a variable minimum voltage needed to provide the requested current to the IPG.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to U.S. Provisional Application62/623,961, filed on Jan. 30, 2018 and incorporated herein by referencein its entirety.

TECHNICAL FIELD

The present technology is directed generally to the efficient use of animplantable pulse generator battery. Some embodiments include usingbattery circuitry to make battery usage by the implantable pulsegenerator more efficient and thereby extend the life of the battery.

BACKGROUND

Neurological stimulators have been developed to treat pain, movementdisorders, functional disorders, spasticity, cancer, cardiac disorders,and various other medical conditions. Implantable neurologicalstimulation systems generally have an implantable signal generator andone or more leads that deliver electrical pulses to neurological tissueor muscle tissue. For example, several neurological stimulation systemsfor spinal cord stimulation (SCS) have cylindrical leads that include alead body with a circular cross-sectional shape and one or moreconductive rings (e.g., contacts) spaced apart from each other at thedistal end of the lead body. The conductive rings operate as individualelectrodes and, in many cases, the SCS leads are implantedpercutaneously through a needle inserted into the epidural space, withor without the assistance of a stylet.

Once implanted, the signal generator applies electrical pulses to theelectrodes, which in turn modify the function of the patient's nervoussystem, such as by altering the patient's responsiveness to sensorystimuli and/or altering the patient's motor-circuit output. In SCStherapy for the treatment of pain, the signal generator applieselectrical pulses to the spinal cord via the electrodes. In conventionalSCS therapy, electrical pulses are used to generate sensations (known asparesthesia) that mask or otherwise alter the patient's sensation ofpain. For example, in many cases, patients report paresthesia as atingling sensation that is perceived as less uncomfortable than theunderlying pain sensation.

In contrast to traditional or conventional (i.e., paresthesia-based)SCS, a form of paresthesia-free SCS has been developed that uses therapysignal parameters that treat the patient's sensation of pain withoutgenerating paresthesia or otherwise using paresthesia to mask thepatient's sensation of pain. One of several advantages ofparesthesia-free SCS therapy systems is that they eliminate the need foruncomfortable paresthesia, which many patients find objectionable.However, a challenge with paresthesia-free SCS therapy systems is thatthe signal may be delivered at frequencies, amplitudes, and/or pulsewidths that use more power than conventional SCS systems. As a result,the battery of the implanted system can discharge and become depleted atan accelerated rate, thereby making battery life an important designconcern.

An additional follow-on challenge with providingnon-paresthesia-generating SCS via an implanted pulse generator is that,in at least some cases, it may be difficult to maintain an effectivesignal as the charge available from the pulse generator batterydecreases. One approach to power consumption challenges in the contextof conventional SCS systems is to increase the frequency with which thepulse generator is charged, but this can be inconvenient for thepatient. Another approach is to add signal conditioning hardware, forexample, to boost the voltage provided by the battery as the batterydischarges. A drawback with this approach is that it can be inefficient.

Yet another follow-on challenge with providingnon-paresthesia-generating SCS via an implanted pulse generator is that,in at least some cases, overcharging or over-discharging the batterybeyond a particular threshold can cause irreversible damage to thebattery and its components. For example, over-discharging the batterybelow a particular threshold can cause “thermal runaway,” whereinbattery charge conditions (e.g., high voltages) can lead toself-sustaining increases in temperature, thereby causing batterycomponents (e.g., the negative electrode or electrolyte) to breakdown.If a battery does go beyond the particular threshold, the battery maybecome unusable and need to be explanted. One approach to overchargingor over-discharging challenges is to avoid passing the particularthresholds beyond which “thermal runaway” occurs by decreasing thecharge rate of the battery as the threshold limits are approached. Thisis often referred to as “trickle charging,” which corresponds to acharge rate less than the typical charge rate used during normaloperation. For example, trickle charging may switch the typical chargerate to the trickle charge rate at a voltage threshold below an upperdamage threshold (UDT) to ensure the UDT is not breached. If the typicalcharge rate for a battery is C/2 (i.e., one-half of the batterycapacity), the trickle charge rate can be, for example, C/5, C/10, C/25,etc. One drawback of this approach is that it can be inefficient, as itcan take longer to charge the battery to a full capacity at a reducedcharge rate. Another drawback of this approach is that it can causedelay and frustration for a patient who may be waiting for the batteryto reach a fully-charged state.

Accordingly, there remains a need for effective and efficient therapysignal delivery, despite the possibility of increased power consumptionresulting from the signal delivery parameters used for paresthesia-freepatient therapy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partially schematic illustration of an implantable spinalcord modulation system positioned at the spine to deliver therapeuticsignals in accordance with embodiments of the present technology.

FIG. 1B is a partially schematic, cross-sectional illustration of apatient's spine, illustrating representative locations for implantedlead bodies in accordance with embodiments of the present technology.

FIG. 2A is a partially schematic isometric view of an implantable signalgenerator having a molded header and a can configured in accordance withembodiments of the present technology.

FIG. 2B is a partially cutaway side view of a portion of the implantablesignal generator of FIG. 2A.

FIG. 3 is a circuit diagram of a therapeutic current-generating circuitthat includes a voltage monitoring circuit in accordance withembodiments of the present technology.

FIG. 4 is a flow diagram illustrating a representative process forautomatically adjusting an electrical signal in accordance withembodiments of the present technology.

FIG. 5 illustrates results from a simulation of the process shown inFIG. 4 .

DETAILED DESCRIPTION

The present technology is directed generally to systems and methods forenhancing usage characteristics of an implantable pulse generator (IPG)battery, which is used in part to deliver electrical signals (alsoreferred to herein as “therapy signals”) to provide patient treatmentvia spinal cord stimulation (SCS) and/or other techniques. For example,in some embodiments, the present technology includes a method ofautomatically adjusting, in a closed loop manner, the value of anelectrical signal parameter. The adjusted parameter can include thevoltage supplied to an electrical signal generating circuit of an IPG.The method can comprise adjusting the value of the electrical signalparameter (e.g., the supply voltage) until receiving an indication thata threshold break has occurred. The threshold break can correspond tothe value of the electrical signal parameter passing below a thresholdvalue, e.g., a value determined to be at or above the minimum valuenecessary to provide effective therapy to the patient. Based at least inpart on the threshold value of the threshold break, the method canfurther comprise increasing the electrical signal parameter by a stepsize and thereafter adjusting (e.g., decreasing) the electrical signalparameter until a subsequent threshold break occurs, e.g., in asubsequent iteration. Each subsequent iteration can decrease thedifference between the supplied electrical signal parameter and aminimum electrical signal parameter needed to deliver adequate therapytreatment to the patient. Accordingly, some embodiments of the presenttechnology can enhance usage characteristics of an IPG to operate thebattery in a more efficient manner and/or decrease the amount ofunnecessary power loss therefrom.

In some embodiments, such as the particular example described above, theiterative process is based on the supply voltage passing below athreshold value. In some embodiments, the iterative process can be basedon a parameter value exceeding a threshold value. Accordingly, unlessotherwise specified, the terms “threshold break” and the like are usedherein to refer to a parameter hitting or passing through a thresholdvalue from above or below.

General aspects of the environments in which the disclosed technologyoperates are described below under Heading 1.0 (“Overview”) withreference to FIGS. 1A, 1B, 2A and 2B. Some embodiments of the technologyare described further under Heading 2.0 (“Representative Embodiments”)with reference to FIGS. 3-5 . While the present technology is describedin the environment of SCS, one with skill in the art would recognizethat one or more aspects of the present technology are applicable toother, non-SCS implantable devices; e.g., more generally, implantableneurostimulators for treatment of one or more patient indications.

1.0 Overview

Some representative examples of paresthesia-free SCS therapy systemsinclude “high frequency” SCS systems. High frequency SCS systems caninhibit, reduce, and/or eliminate pain via waveforms with high frequencyelements or components (e.g., portions having high fundamentalfrequencies), generally with reduced or eliminated side effects. Suchside effects can include unwanted paresthesia, unwanted motorstimulation or blocking, unwanted pain or discomfort, and/orinterference with sensory functions other than the targeted pain. Insome embodiments, a patient may receive high frequency therapeuticsignals with at least a portion of the therapy signal at a frequency offrom about 1.2 kHz to about 100 kHz, or from about 1.5 kHz to about 50kHz, or from about 3 kHz to about 20 kHz, or from about 5 kHz to about15 kHz, or at frequencies of about 8 kHz, 9 kHz, or 10 kHz. Thesefrequencies are significantly higher than the frequencies associatedwith conventional “low frequency” SCS, which are generally below 1,200Hz, and more commonly below 100 Hz. Accordingly, modulation at these andother representative frequencies (e.g., from about 1.2 kHz to about 100kHz) is occasionally referred to herein as “high frequency stimulation,”“high frequency SCS,” and/or “high frequency modulation.”

FIG. 1A schematically illustrates a representative patient therapysystem 100 for providing relief from chronic pain and/or otherconditions, arranged relative to the general anatomy of a patient'sspinal column 191. The system 100 can include a signal generator 101(e.g., an implanted pulse generator or IPG), which may be implantedsubcutaneously within a patient 190 and coupled to one or more signaldelivery elements or devices 110. The signal delivery elements ordevices 110 may be implanted within the patient 190, typically at ornear the patient's spinal cord midline 189. The signal delivery elements110 carry features for delivering therapy to the patient 190 afterimplantation. The signal generator 101 can be connected directly to thesignal delivery devices 110, or it can be coupled to the signal deliverydevices 110 via a signal link or lead extension 102. In someembodiments, the signal delivery devices 110 can include one or moreelongated lead(s) or lead body or bodies 111 (identified individually asa first lead 111 a and a second lead 111 b). As used herein, the termssignal delivery device, lead, and/or lead body include any of a numberof suitable substrates and/or support members that carryelectrodes/devices for providing therapy signals to the patient 190. Forexample, the lead or leads 111 can include one or more electrodes orelectrical contacts that direct electrical signals into the patient'stissue, e.g., to provide for therapeutic relief. In some embodiments,the signal delivery elements 110 can include structures other than alead body (e.g., a paddle) that also direct electrical signals and/orother types of signals to the patient 190.

In some embodiments, one signal delivery device may be implanted on oneside of the spinal cord midline 189, and a second signal delivery devicemay be implanted on the other side of the spinal cord midline 189. Forexample, the first and second leads 111 a, 111 b shown in FIG. 1A may bepositioned just off the spinal cord midline 189 (e.g., about 1 mmoffset) in opposing lateral directions so that the two leads 111 a, 111b are spaced apart from each other by about 2 mm. In some embodiments,the leads 111 may be implanted at a vertebral level ranging from, forexample, about T8 to about T12. In some embodiments, one or more signaldelivery devices can be implanted at other vertebral levels, e.g., asdisclosed in U.S. Pat. No. 9,327,121, which is incorporated by referenceherein in its entirety.

The signal generator 101 can transmit signals (e.g., electrical signals)to the signal delivery elements 110 that up-regulate (e.g., excite)and/or down-regulate (e.g., block or suppress) target nerves. As usedherein, and unless otherwise noted, the terms “modulate,” “modulation,”“stimulate,” and “stimulation” refer generally to signals that haveeither type of the foregoing effects on the target nerves. The signalgenerator 101 can include a machine-readable (e.g., computer-readable)or controller-readable medium containing instructions for generating andtransmitting suitable therapy signals. The signal generator 101 and/orother elements of the system 100 can include one or more processor(s)107, memory unit(s) 108, and/or input/output device(s) 112. Accordingly,the process of providing modulation signals, providing guidanceinformation for positioning the signal delivery devices 110,establishing battery charging and/or discharging parameters, and/orexecuting other associated functions can be performed bycomputer-executable instructions contained by, on or incomputer-readable media located at the pulse generator 101 and/or othersystem components. Further, the pulse generator 101 and/or other systemcomponents may include dedicated hardware, firmware, and/or software forexecuting computer-executable instructions that, when executed, performany one or more methods, processes, and/or sub-processes describedherein; e.g., the methods, processes, and/or sub-processes describedwith reference to FIGS. 2-5 below. The dedicated hardware, firmware,and/or software also serve as “means for” performing the methods,processes, and/or sub-processes described herein. The signal generator101 can also include multiple portions, elements, and/or subsystems(e.g., for directing signals in accordance with multiple signal deliveryparameters), carried in a single housing, as shown in FIG. 1A, or inmultiple housings.

The signal generator 101 can also receive and respond to an input signalreceived from one or more sources. The input signals can direct orinfluence the manner in which the therapy, charging, and/or processinstructions are selected, executed, updated, and/or otherwiseperformed. The input signals can be received from one or more sensors(e.g., an input device 112 shown schematically in FIG. 1A for purposesof illustration) that are carried by the signal generator 101 and/ordistributed outside the signal generator 101 (e.g., at other patientlocations) while still communicating with the signal generator 101. Thesensors and/or other input devices 112 can provide inputs that depend onor reflect patient state (e.g., patient position, patient posture,and/or patient activity level), and/or inputs that arepatient-independent (e.g., time). Still further details are included inU.S. Pat. No. 8,355,797, incorporated by reference herein in itsentirety.

In some embodiments, the signal generator 101 and/or signal deliverydevices 110 can obtain power to generate the therapy signals from anexternal power source 103. In some embodiments, for example, theexternal power source 103 can by-pass an implanted signal generator andgenerate a therapy signal directly at the signal delivery devices 110(or via signal relay components). The external power source 103 cantransmit power to the implanted signal generator 101 and/or directly tothe signal delivery devices 110 using electromagnetic induction (e.g.,RF signals). For example, the external power source 103 can include anexternal coil 104 that communicates with a corresponding internal coil(not shown) within the implantable signal generator 101, signal deliverydevices 110, and/or a power relay component (not shown). The externalpower source 103 can be portable for ease of use.

In some embodiments, the signal generator 101 can obtain the power togenerate therapy signals from an internal power source, in addition toor in lieu of the external power source 103. For example, the implantedsignal generator 101 can include a non-rechargeable battery or arechargeable battery to provide such power. When the internal powersource includes a rechargeable battery, the external power source 103can be used to recharge the battery. The external power source 103 canin turn be recharged via a suitable power source (e.g., conventionalwall power).

During at least some procedures, an external stimulator or trialmodulator 105 can be coupled to the signal delivery elements 110 duringan initial procedure, prior to implanting the signal generator 101. Forexample, a practitioner (e.g., a physician and/or a companyrepresentative) can use the trial modulator 105 to vary the modulationparameters provided to the signal delivery elements 110 in real time,and select optimal or particularly efficacious parameters. Theseparameters can include the location from which the electrical signalsare emitted, as well as the characteristics of the electrical signalsprovided to the signal delivery devices 110. In some embodiments, inputis collected via the external stimulator or trial modulator and can beused by the clinician to help determine what parameters to vary. In atypical process, the practitioner uses a cable assembly 120 totemporarily connect the trial modulator 105 to the signal deliverydevice 110. The practitioner can test the efficacy of the signaldelivery devices 110 in an initial position. The practitioner can thendisconnect the cable assembly 120 (e.g., at a connector 122), repositionthe signal delivery devices 110, and reapply the electrical signals.This process can be performed iteratively until the practitioner obtainsthe desired position for the signal delivery devices 110. Optionally,the practitioner may move the partially implanted signal deliverydevices 110 without disconnecting the cable assembly 120. Furthermore,in some embodiments, the iterative process of repositioning the signaldelivery devices 110 and/or varying the therapy parameters may not beperformed.

The signal generator 101, the lead extension 102, the trial modulator105 and/or the connector 122 can each include a receiving element 109.Accordingly, the receiving elements 109 can be patient implantableelements, or the receiving elements 109 can be integral with an externalpatient treatment element, device or component (e.g., the trialmodulator 105 and/or the connector 122). The receiving elements 109 canbe configured to facilitate a simple coupling and decoupling procedurebetween the signal delivery devices 110, the lead extension 102, thepulse generator 101, the trial modulator 105 and/or the connector 122.The receiving elements 109 can be at least generally similar instructure and function to those described in U.S. Patent ApplicationPublication No. 2011/0071593, incorporated by reference herein in itsentirety.

After the signal delivery elements 110 are implanted, the patient 190can receive therapy via signals generated by the trial modulator 105,generally for a limited period of time. During this time, the patientwears the cable assembly 120 and the trial modulator 105 outside thebody. Assuming the trial therapy is effective or shows the promise ofbeing effective, the practitioner then replaces the trial modulator 105with the implanted signal generator 101, and programs the signalgenerator 101 with therapy programs selected based on the experiencegained during the trial period. Optionally, the practitioner can alsoreplace the signal delivery elements 110. Once the implantable signalgenerator 101 has been positioned within the patient 190, the therapyprograms provided by the signal generator 101 can still be updatedremotely via a wireless physician's programmer 117 (e.g., a physician'slaptop, a physician's remote or remote device, etc.) and/or a wirelesspatient programmer 106 (e.g., a patient's laptop, patient's remote orremote device, etc.). Generally, the patient 190 has control over fewerparameters than does the practitioner. For example, the capability ofthe patient programmer 106 may be limited to starting and/or stoppingthe signal generator 101, and/or adjusting the signal amplitude. Thepatient programmer 106 may be configured to accept pain relief input aswell as other variables, such as medication use.

In any of the foregoing embodiments, the parameters in accordance withwhich the signal generator 101 provides signals can be adjusted duringportions of the therapy regimen. For example, the frequency, amplitude,pulse width, and/or signal delivery location can be adjusted inaccordance with a pre-set therapy program, patient and/or physicianinputs, and/or in a random or pseudorandom manner. Such parametervariations can be used to address a number of potential clinicalsituations. Certain aspects of the foregoing systems and methods may besimplified or eliminated in some embodiments of the present disclosure.Further aspects of these and other expected beneficial results aredetailed in U.S. Pat. No. 9,327,121 (previously incorporated byreference), U.S. Pat. Nos. 8,712,533, and 9,592,388, and U.S. PatentApplication Publication No. 2009/0204173, all of which are incorporatedherein by reference in their entireties.

FIG. 1B is a cross-sectional illustration of the spinal cord 191 and anadjacent vertebra 195 (based generally on information from Crossman andNeary, “Neuroanatomy,” 1995 (published by Churchill Livingstone)), alongwith multiple leads 111 (shown as leads 111 a-111 e) implanted atrepresentative locations. For purposes of illustration, multiple leads111 are shown in FIG. 1B implanted in a single patient. In actual use,any given patient will likely receive fewer than all the leads 111 shownin FIG. 1B.

The spinal cord 191 is situated within a vertebral foramen 188, betweena ventrally located ventral body 196 and a dorsally located transverseprocess 198 and spinous process 197. Arrows V and D identify the ventraland dorsal directions, respectively. The spinal cord 191 itself islocated within the dura mater 199, which also surrounds portions of thenerves exiting the spinal cord 191, including the ventral roots 192,dorsal roots 193 and dorsal root ganglia 194. The dorsal roots 193 enterthe spinal cord 191 at the dorsal root entry zone 187, and communicatewith dorsal horn neurons located at the dorsal horn 186. In oneembodiment, the first and second leads 111 a, 111 b are positioned justoff the spinal cord midline 189 (e.g., about 1 mm. offset) in opposinglateral directions so that the two leads 111 a, 111 b are spaced apartfrom each other by about 2 mm, as discussed above. In other embodiments,a lead or pairs of leads can be positioned at other locations, e.g.,toward the outer edge of the dorsal root entry zone 187 as shown by athird lead 111 c, or at the dorsal root ganglia 194, as shown by afourth lead 111 d, or approximately at the spinal cord midline 189, asshown by a fifth lead 111 e.

FIG. 2A is a partially schematic isometric view of an implantable signalgenerator 200 (e.g., an IPG), and FIG. 2B is a partially cutaway sideview of a portion of the implantable signal generator 200. Referringfirst to FIGS. 2A, the signal generator 200 includes a header 202, and acan 204 attached to the header 202. The can 204 may include a shell 206and a lid 208 positioned at least partially between the header 202 andthe can 204. Referring next to FIG. 2B, the lid 208 can include aplurality of feed-throughs 212 for electrical communication between theheader 202 and the can 204. The header 202 can carry a charging coil224, a communication antenna 222, and one or more receiving elements216. The receiving elements 216 can include a plurality of outputterminals or contact assemblies 218 configured to provide electricalconnections to the signal delivery devices 110 or the lead extension102.

Multiple wires 226 can extend upwardly from the can 204 through thefeed-throughs 212 and couple to (a) individual contact assemblies 218,(b) the communication antenna 222, or (c) the charging coil 224. Thewires 226 can provide electrical connections between components withinthe header 202, e.g., the charging coil 224 and the communicationantenna 222, and components within the can 204, e.g., a battery 230, acontroller 232, etc. The battery 230 can be electrically coupled to thecontroller 232 and the output terminals or contact assemblies 218 toprovide electrical power to the implantable signal generator 200 via thereceiving elements 216. The battery 230 can be recharged via anelectrical coupling to the charging coil 224. The controller 232 can beelectrically coupled to the contact assemblies 218 and the battery 230,and can include a processor 234, memory 236, electronic circuitry, andother electronic components for controlling and/or operating theimplantable signal generator 200. In operation, the charging coil 224can convert electromagnetic energy (e.g., a magnetic flux) intoelectrical current to charge the battery 230. The communication antenna222 can receive signals associated with operating and/or controlling theimplantable signal generator 200. For example, control signals to updateoperating parameters (e.g., the frequency, amplitude and/or duration ofmodulation signals) for the implantable signal generator 200 can bereceived by the communications antenna 222 and sent to the controller232. The controller 232 can control the delivery of electrical power tothe receiving elements 216.

The header 202 includes a first access seal 217 a and a second accessseal 217 b (collectively referred to as the access seals 217). Theaccess seals 217 include a self-sealing entrance point to provide accessfor a tool (e.g., a screwdriver) to secure a connection (e.g., a screw)to the signal delivery device 110 (FIG. 1A) or the lead extension 102(FIG. 1A) via the set-screw blocks 219. The access seals 217 can beformed from a pliable silicone or other suitable material such that thetool can pass through and expand the entrance point. When the tool iswithdrawn, the entrance point can automatically close to reduce oreliminate the possibility of any foreign material (e.g., blood or otherbodily fluids) subsequently entering into the header 202.

Computer readable instructions contained in the memory 236 can includeoperating parameters and instructions to control the operation of theimplantable signal generator 200. Specifically, the implantable signalgenerator 200 can include battery charging integrated circuits (IC) tomonitor battery status and protect the battery against overchargingand/or over-discharging, thereby decreasing the chance of irreversibledamage to the battery. The battery charging IC can comprise batteryprotection circuitry that includes (a) battery-charging circuitryelectrically coupling the battery to power sources and/or othercomponents configured to charge the battery, and (b) battery-loadcircuitry electrically coupling the battery to the implantable signalgenerator 200 and/or other components configured to discharge or drainthe battery. In some embodiments, the battery charging IC can includeone or more switches, e.g., field effect transistors (FETs), set toautomatically open and/or close in order to maintain the charging anddischarging parameter values (e.g., voltages) of the battery withinpreset battery operating parameter limits. The battery charging IC cansimilarly include one or more fuses set to maintain the charging anddischarging current values of the battery within preset currentparameter limits. As described in further detail below, the batteryprotection circuitry can be set to ensure operating battery voltageand/or current do not exceed or fall below corresponding thresholds.

2.0 Representative Embodiments Establishing Battery Charging andDischarging Parameters to Extend Battery Life

Systems of the type described above with reference to FIGS. 1A-2B caninclude IPGs having rechargeable batteries or other rechargeable powersources that are periodically recharged with an external charger. Overthe course of a given therapeutic regimen, the patient and/or thepractitioner may change the parameters in accordance with which theelectrical signals are delivered to the patient. As the parameterschange, the rate at which electrical current is drawn or drained fromthe battery can also change. In addition, different patients may chargetheir batteries in accordance with different schedules, and/or may varyin the consistency with which they adhere to such schedules. Stillfurther, the characteristics of the rechargeable battery can change overthe course of time. For example, the overall charge capacity (C) of thebattery will typically decrease over time, e.g., due to chemicaldegradation. Techniques in accordance with the present technology,described further below, can tailor the manner in which the battery ischarged and/or discharged by taking into account one or more of theforegoing variables to increase the usable life of the battery, and/orcan be applied generally, e.g., without patient specific parameters.

As previously described, irreversible damage of the battery components,e.g., the negative electrode or electrolyte, can occur if the battery isover-discharged below or overcharged above particular thresholds. Forexample, over-discharging the battery below a lower damage threshold(LDT), and/or overcharging the battery above an upper damage threshold(UDT) can cause “thermal runaway,” thereby potentially causing at leasta portion of the battery components to break down. In some embodiments,the LDT for a lithium-ion battery having a nominal voltage output ofapproximately 3.6V, may be at approximately 2.75V+/−0.2V, and the UDTfor lithium-ion battery may be at approximately 4.1V+/−0.2V. In lieu ofor in addition to the voltage thresholds, the LDT and/or UDT can bebased on current. The present technology provides methods forestablishing charge parameters for a battery-powered implantable medicaldevice to avoid over-discharging a battery below the LDT and/orovercharging a battery above the UDT, while also maintaining efficientcharging parameters for convenience of the patient.

In some embodiments, there is provided a method for establishing chargeparameters for a battery-powered implantable medical device, wherein thebattery is charged at a constant primary charge rate (PCR) over thenormal operating range of the battery. The PCR is intended to representa charge rate considered to most efficiently charge the battery. Forexample, the PCR can correspond to the highest charge rate thatmaintains a minimum level of risk that damage to the battery will occurduring charging. In one non-limiting example, the battery may be chargedat a PCR of approximately C/2 (e.g., half of the battery capacity) atleast within a normal operating range of the battery. In someembodiments, the PCR may be C/3, C/4, etc.

In some embodiments, the normal operating range of the battery can befrom (a) a lower operating threshold (LOT) set above, or slightly above(e.g., less than 10% above) the LDT, to an upper operating threshold(UOT) set below (e.g., slightly below) the UDT. For a battery having anominal output voltage of approximately 3.6V, the LOT can vary fromapproximately 3.1V to approximately 3.3V, and the UOT can vary fromapproximately 3.9V to approximately 4.1V. The LOT and UOT can preventthe battery from reaching the LDT and UDT, respectively, and therebyprevent or inhibit irreversible damage to the battery. As the batteryapproaches, but does not surpass, one of the LOT or the UOT, batteryprotection circuitry of the IPG can maintain the charging rate at thePCR. As such, the battery protection circuitry may not include ortransition to the trickle charge rate previously described. Oneadvantage of having a constant PCR in combination with battery chargingcircuitry is that, compared to a traditional IPG that automaticallyswitches to a trickle charge rate, the battery can experience a fastercharge while still maintaining protection to prevent irreversible damageto the battery. As a result, the present technology makes more effectiveuse of the patient's time, as the patient does not need to wait for theadditional time needed during the “trickle charge” phase to fully-chargethe battery.

Unlike traditional batteries that transition to a trickle charge rate asbattery threshold limits are approached, the battery charging IC of thepresent technology can be configured to automatically disconnect thebattery from battery-charging circuitry or the battery-load circuitry.For example, the battery protection circuitry can automaticallydisconnect the battery from the battery-charging circuitry once the UOTis reached or nearly reached to prevent or inhibit the battery voltagefrom reaching or surpassing the UDT. In some embodiments, powertransmitted to the battery will not be received, and thus will notaffect the operating voltage or operating current of the battery. Assuch, when the battery reaches or nearly reaches the UOT and is thusconsidered fully charged, any patient-initiated further charge will beprohibited via the battery charging IC, or more specifically by openingswitches and/or fuses of the battery charging circuitry.

Similarly, as the battery discharges and the LOT is reached or nearlyreached, the battery protection circuitry can automatically disconnectat least a portion of the battery from the battery-load circuitry toprevent or inhibit the battery voltage from reaching or falling belowthe LDT. In some embodiments, a load or a portion of the load beingdrawn from the battery ceases. For example, in some embodiments, certainfunctions of the IPG, e.g., signal delivery functions and telemetryfunctions, may cease. As such, when the battery charge reaches or nearlyreaches the LOT and is thus considered discharged to a minimum operatingrange, any further load request made to the battery may be ignored. Morespecifically, the switches and/or fuses of the battery chargingcircuitry may open once the battery charge reaches the LOT, therebycausing the IPG to lose at least a portion of its ability to furtherdrain the battery. In some embodiments, while certain functions of theIPG may cease, other functions, e.g., a clock function, of the IPG maycontinue to be operational, thereby allowing the patient and/or operatorto monitor diagnostics of the IPG even after the battery charge hasdischarged at or below the LOT. As a result, these other functions ofthe IPG that continue to be operational may cause the battery charge tofurther discharge, but at a slower rate. For example, once the LOT isreached, the current draw of the battery may be decreased, therebyallowing the battery charge to remain above the LDT or another thresholdlimit for a few weeks.

In some embodiments wherein the battery is discharging and approachingthe LOT, the battery charging IC may include a second lower operatingthreshold (SLOT) between the LOT and LDT. The SLOT may function as afurther precaution to ensure the battery charge does not reach the LDT,and can vary within a range from approximately 2.8V+/−0.2V toapproximately 3.1V+/−0.2V, or within a narrower or broader rangedepending on the corresponding LOT and LDT. As previously stated, oncethe LOT is reached, certain functions of the IPG may cease. Once theSLOT is reached, the IPG may then be completely disconnected fromremaining functions of the IPG, and placed into a hibernation stateintended to prevent the battery from discharging further. As such, thebattery may continue to discharge, but at an even slower rate than thedischarge rate after the LOT is reached. Once the SLOT is reached, thecurrent draw of the battery may be at an absolute minimum, and in someembodiments, can allow the battery charge to remain above the LDT forapproximately 6-9 months or longer, depending on the margin between theSLOT and LDT.

The LDT, SLOT, LOT, UOT and UDT can each be set such that a minimummargin is maintained between a neighboring threshold. For example, theSLOT may be set at a preset margin, e.g., 1%, 5%, 10%, etc., above theLDT, and the LOT may be set at a preset margin, e.g., 1%, 5%, 10%, etc.,above the SLOT. Similarly, the UOT may be set at a preset margin, e.g.,1%, 5%, 10%, etc., below the UDT. Naturally, a higher margin betterensures that the LDT and/or UDT will not be reached, and thatirreversible damage to the battery will not occur. The preset LOT-LDTmargin and the UOT-UDT margin, can be the same, e.g., both can be set to5%, or they can differ, e.g., the LOT-LDT margin can be set to 10% andthe UOT-UDT margin can be set to 5%. Setting the LOT-LDT margin highermay be preferred to ensure any disruption of patient therapy is avoided.Also, setting the LOT-LDT margin higher can be beneficial because of theinherent self-discharge of batteries that can cause the operatingvoltage to further decrease even after the battery charging circuitryelectrically disconnects the battery from the surrounding systemcomponents.

One feature of at least some embodiments is that the processes forestablishing and/or adjusting the charge and/or discharge parameters canbe automated. An advantage of this feature is that it can reduce oreliminate the effort on the part of the patient and/or the practitionerand/or the company representative to achieve the benefits of tailoredcharge/discharge parameters. Still another advantage of the foregoingfeatures is that, in some embodiments, the patients perception of theconsistency of the system can be improved. For example, by automaticallyproviding and adjusting (as needed) the margins within which the IPGbattery operates, the patient will be less likely to over-discharge thebattery.

Another feature of at least some embodiments is that processes forestablishing and/or adjusting the charge and/or discharge parameters canbe tailored, adjusted, determined, calculated, set, or otherwiseestablished in a manner that reflects patient-specific and/orbattery-specific characteristics. The battery characteristics caninclude the age of the battery, the number of charge cycles undergone bythe battery, the total amount of charge delivered by the battery (e.g.,over many charge cycles), and/or other aspects of the battery that mayvary from one patient's IPG to another patient's IPG. As anotherexample, an older battery and/or a battery that has been charged anddischarged many times will typically have a lower total charge capacitythan a battery that is new and/or has undergone fewer charge/dischargecycles. The data corresponding to these characteristics can be stored atthe IPG and updated periodically. For example, the IPG can store themanufacture date of the battery. Each time the battery is charged, theIPG can increment a battery charge counter. Further aspects of these andother expected beneficial results are detailed in U.S. PatentApplication Publication No. 2016/0114171 which is incorporated byreference herein in its entirety.

Enhancing Usage Characteristics of an IPG Battery

FIG. 3 shows a simplified block diagram of an implantable therapeuticdevice 300 (e.g., an IPG) configured in accordance with an someembodiments of the present technology. The implantable device 300includes a current-generating circuit 302 (labelled current generator)that produces therapeutic currents for one or more electrode leads 340or other signal delivery device(s). The therapeutic device furtherincludes a rechargeable battery 304 and an inductive charging circuit306 that is used to recharge the battery 304 from an external charger(e.g., external power source 103 from FIG. 1A). Alternatively, thebattery 304 may be a single-use battery that must be periodicallyreplaced. The therapeutic device also includes a logic circuit orprocessor (CPU) 310 (e.g., a microprocessor, a microcontroller, digitalsignal processor FPGA, ASIC or the like). Voltage from the battery 304is supplied to a programmable voltage regulator 308 that produces avariable supply voltage to the current-generating circuit 302 under thecontrol of the processor 310. In some embodiments, the battery 304 is alithium-ion battery that produces a voltage of approximately 3.2 voltswhen fully charged. The programmable voltage regulator 308 can increasethis voltage to a higher level (e.g., 4-20 volts) or can decrease thevoltage, e.g., down to approximately 2.0 volts or lower.

In some embodiments, the processor 310 is programmed to send signals tothe programmable voltage regulator 308 to adjust the voltage supplied tothe current generating circuit 302 so that the current generatingcircuit 302 can supply a requested current to the electrodes on thelead(s) 340 but not supply a voltage that is so high that battery poweris wasted.

A programmable switch assembly 314 in the implantable device 300 is usedto configure connections to the electrodes 342 a-c (collectively“electrodes 342”) on the leads 340 in order to control how the requestedcurrent is delivered to the patient. The switch assembly 314 iscontrolled by the processor 310 so that currents can be deliveredbetween any of the electrodes 342 on the lead (e.g., between one or more“anode” contacts and one or more “cathode” contacts to operate thedevice in a bi-polar or other multi-polar manner). Alternatively, theprogrammable switch assembly 314 can configure the connections to thecontacts so that currents flow between one or more of the contacts 342and a remote common electrode or contact (such as the case of theimplantable device) in order to operate the contacts 342 in a uni-polarmanner.

In some embodiments, the implantable device 300 includes a wirelesscommunication circuit 320 that transmits and receives signals from anexternal programmer (e.g., the patient programmer 106, the physician'sprogrammer 117 shown in FIG. 1A), in order to control the therapies thatare delivered to the patient, to supply a doctor or technician withinformation about the operation of the device, to update the operatingprogram or parameters of the device and for other uses. Additionaldetails of current generator circuits and related information areprovided in U.S. Patent Application Publication No. 2017/0197079, whichis incorporated by reference herein in its entirety.

As discussed above, it is desirable that the voltage supplied by theprogrammable voltage regulator 308 is sufficient to allow thecurrent-generating circuit 302 to generate the requested currents fordelivery to the contacts. On the other hand, if the voltage supplied tothe current-generating circuit is more than the voltage needed, batterypower is wasted and battery power will be depleted unnecessarily. Thepresent technology includes methods and systems configured to managethese competing technologies.

FIG. 4 is a flow diagram illustrating a representative process 400 forenhancing usage characteristics of an IPG battery in accordance withsome embodiments of the present technology. Process 400 generallycomprises operations for iteratively tuning a supplied voltage, V_(S),to minimize its difference from a minimum required voltage, V_(MIN),needed to deliver adequate therapy treatment to the patient. In a firstiteration of a closed loop, the system causes V_(S) to approach V_(MIN)according to a set of operating parameters until V_(S) is equal to orless than a threshold value, V_(TH), which is above V_(MIN). A thresholdbreak occurs at the point in time when V_(S) is approximately equal toor slightly below V_(TH). Based on this threshold break, the system canadjust V_(S) (e.g., by a step size) and operating parameters for asubsequent iteration of the closed loop. This process can then berepeated, with updated V_(S) values and updated operating parameters forsubsequent iterations being based on one or more of the previousthreshold breaks. Generally speaking, this process allows V_(S) to trackV_(MIN) to reduce or eliminate power loss resulting from a higher thannecessary V_(S).

Process portion 402 includes determining and/or obtaining a minimumoperating voltage, V_(MIN). As previously described, V_(MIN) cancorrespond to the minimum voltage that needs to be supplied to acurrent-generating circuit for it to deliver a requested current toelectrodes on one or more leads connected to the IPG. V_(MIN) and/or therequested current from the current generating circuit are functions ofimpedance and can vary based on multiple factors, including theparticular therapy requested or delivered at a given time, patientmovement, patient posture, patient activity level, etc. In someembodiments, determining V_(MIN) on a continuous basis can causesignificant power to be drawn from the IPG battery. Accordingly, in someembodiments, process portion 402 may be omitted from the process 400.

Process portion 404 includes delivering or supplying a supply voltage,V_(S), to the current-generating circuit, which then uses V_(S) todeliver a requested current to the patient as therapy. When a therapysession is first initiated, the specific value of V_(MIN) may not beknown, and thus V_(S) may be supplied at a default value that is highenough to ensure it is above most or all possible V_(MIN) values. Thetherapy (e.g., at the requested current) can then be delivered to thepatient. As such, V_(S) may initially operate at a level (e.g., 10V)that is significantly above V_(MIN). Alternatively, in some embodiments,V_(S) may correspond to a particular voltage from a previous therapytreatment for that patient and the particular impedance. For example, ifthe processor associated with the IPG assimilates an impedance profilefor the current treatment with a similar impedance profile from aprevious treatment, the processor can input the V_(S) value previouslyused as the initial V_(S) value for the current treatment. In someembodiments, the V_(S) value may be accessed via a database of impedanceprofiles corresponding to that particular patient or other patients whohad similar therapy treatments. Using these previous V_(S) values canaid in reducing the excess power loss typically seen when a therapytreatment session is initiated at a high V_(S) level.

Process portion 406 includes adjusting V_(S) according to a set ofoperating parameters. The operating parameters, for example, can includea rate (e.g., volts/millisecond) at which V_(S) is to be increased ordecreased in order to cause a threshold break, as previously described.As discussed above, when a therapy session is first initiated, V_(MIN)may not be known, and thus the relationship between V_(MIN) and V_(S)may also not be known. As such, the initial operating parameters for thefirst iteration of the closed loop may be default values that, forexample, result in V_(S) decreasing along a negative slope until V_(S)approximately equals or falls below the threshold value, V_(TH). In someembodiments, the operating parameters may be based on operating valuesfrom previous treatments, and accordingly the process 400 may referencethe database of impedance profiles, as previously described. Asexplained in further detail with reference to FIG. 5 , the operatingparameters for a single iteration (e.g., process portions 404, 406, 408,and 410) of a closed loop may be based on operating parameters from animmediately previous iteration or multiple previous iterations (e.g.,the two preceding iterations or three preceding iterations).

In some embodiments, process portion 406 can include adjusting (e.g.,increasing or decreasing) or holding a V_(S) value until and if anindication of a threshold break is received (process portion 408) by thesystem, or until a preset time has elapsed without a threshold breakhaving occurred (process portion 412). As previously mentioned, athreshold break can include a moment in time at which V_(S) equals orfalls below V_(TH). For example, if V_(MIN) is equal to 2V, and thesystem includes a preferred operating margin of 0.5V, then the thresholdlimit would be 2.5V. As such, the system would receive an indication ofa threshold break if and when V_(S) falls below the threshold limit of2.5V as V_(S) is being decreased according to process portion 406. Thecharacteristics accompanying the threshold break (e.g., the V_(S) valueat the threshold break, the time elapsed since the previous thresholdbreak, etc.), in addition to the characteristics of the previousthreshold breaks, can then provide a basis for altering V_(S) and/or theoperating parameters (e.g., process portion 410) for a subsequentiteration of the closed loop. As such, in some embodiments, if and whenan indication of a threshold break is received, new values for V_(S) andthe operating parameters can be sent to the processor to be used in thesubsequent iteration. For example, process portion 410 includesadjusting V_(S) and/or the operating parameters for the process portion404 for the subsequent iteration. In practice, when the next iterationis initiated (e.g., after a threshold break or elapsed time), the V_(S)profile will experience an initial step corresponding to the newlyadjusted V_(S) value, followed by an increase, decrease, or hold ofV_(S) corresponding to the newly adjusted operating parameters. Witheach iterative adjustment made to the V_(S) value and the operatingparameters, the voltage difference between V_(MIN) and V_(S) can bedecreased at least because the profile of V_(MIN) becomes betterunderstood and V_(S) can be adjusted to more closely reflect V_(MIN).

In some embodiments, a threshold break may not occur within an elapsedtime. In such embodiments, after the elapsed time since adjusting V_(S)via process portion 406, the process 400 can proceed to process portion414 (process portion 412). Process portion 412 can help ensure a minimumtime has passed before any subsequent closed loop begins. In someembodiments where the process 400 proceeds to process portion 404 viaprocess portion 414 (i.e., without receiving indication of a thresholdbreak at process portion 408), V_(S) and/or the operating parameters maybe adjusted in predetermined manner for the next iteration.

FIG. 5 illustrates a plot 500 depicting a simulation of a representativeprocess described in FIG. 4 . The y-axis corresponds to voltage (e.g.,measured voltage), and the x-axis corresponds to time (e.g.milliseconds). A first line (shown in dot-dash format) corresponds toV_(MIN), a second line (shown solid) corresponds to V_(TH), and a thirdline (shown dashed) corresponds to V_(S). As previously described withreference to FIG. 4 , V_(S) can be continuously adjusted according tothe iterative operations of (1) supplying V_(S) for a first iteration ofa closed loop, (2) adjusting V_(S) according to operating parameters forthe first iteration, (3) receiving an indication of a threshold breakresulting from V_(S) equaling or falling below V_(TH), (4) after thethreshold break, determining and adjusting V_(S) and operatingparameters for a subsequent iteration of the closed loop, and (5)iteratively repeating the operations of (1), (2), (3), and (4) astherapy continues to be delivered to the patient. As shown in FIG. 5 ,the simulation illustrated includes a first portion 502 having arelatively steady V_(MIN) profile, a second portion 503 having anincreasing V_(MIN) profile, and a third portion 504 having a decreasingV_(MIN) profile. In some embodiments, each of these portions 502, 503,504 can correspond to different algorithms used to determine thecorresponding supply voltage and operating parameters.

Starting at the first iteration (1) shown in FIG. 5 , V_(S) is initiallyset to a default value that is greater than V_(TH) and V_(MIN), and thendecreases along path 510 according to a set of default operatingparameters. Upon reaching V_(TH), the system indicates a first thresholdbreak. As previously described, the threshold break can correspond to avalue slightly above (e.g., 10% above) a corresponding value for atherapy interruption, which can correspond to a value at which thecurrent generator circuit of the IPG cannot supply adequate currentand/or therapy to the patient. The threshold break can be used as abreak point to adjust V_(S) before actual therapy is interrupted (e.g.,if V_(S) fell below V_(MIN)). Based on the first threshold break, thesystem determines an increased V_(S) value and/or adjusted operatingparameters to be used in the second iteration (2). The system may alsostore the V_(S) value at which the first threshold break occurred, asthis value can be used to help determine V_(S) and operating parametervalues for subsequent iterations (e.g., the third iteration). Followingthe first iteration (1), the second iteration (2) begins by adjustingV_(S) to the most recently sent (e.g., inputted) V_(S) value, resultingin a V_(S) step 512. The system then decreases V_(S) along path 514according to the most recently sent operating parameters, which thenresults in a second threshold break. The V_(S) value associated withstep 512 is closer to V_(MIN), compared to the previous starting V_(S)value for the first iteration (1), and the slope of the path 514 moreclosely mirrors the V_(MIN) profile, compared to the slope of theprevious V_(S) path 510. Following the second threshold break, thesystem can consider and/or store the V_(S) values for the first andsecond threshold breaks, and can follow a similar set of operations forthe third iteration (3).

As shown by the first portion 502 of the simulation, the system allowsV_(S) to continually approach and track V_(MIN) with each subsequentiteration. For example, the V_(S) step value for each subsequentiteration can be closer to V_(MIN) than the step value for the precedingiteration. Additionally, the operating parameters for each subsequentiteration can result in a slope that more closely reflects the slope ofV_(MIN), compared to the slope of the preceding iteration. As such, thesystem is iteratively tuned to decrease power loss from the system(e.g., via dissipated heat) with each additional iteration that isperformed. In part, this is because each additional iteration andthreshold break provide further data about the profile of V_(MIN) to thesystem. For example, the V_(S) step value and operating parametersinputted and used for the fourth iteration (4) can be based on thefirst, second, and/or third threshold breaks, as opposed to the V_(S)step value and operating parameters used for the second iteration (2),which may only be based on the first threshold break. As such, eachadditional iteration allows the system to develop a more accurateprofile of V_(MIN) and its increasing, decreasing, or steadycharacteristics or rate of change.

The second portion 503 of the plot 500 corresponds to an increasingV_(MIN) profile. Here, the third threshold break following the thirditeration (3) indicates to the system that V_(MIN) is slightlyincreasing, at least because V_(MIN) at the third threshold break ishigher than V_(MIN) at the second threshold break. As such, the systemcan determine that the change of V_(MIN) from the second to thirdthreshold breaks is slightly greater than the change of V_(MIN) from thefirst to second threshold breaks. Based on the previous first, secondand/or third threshold breaks, the system can provide adjusted valuesfor V_(S) and operating parameters to be used in the fourth iteration(4). The V_(S) step 530 for the fourth iteration (4) may be similar tothe V_(S) step 516 for the third iteration (3) because the system hasenough data points now to predict that the V_(MIN) is increasing. Forsimilar reasons, the operating parameters used for the fourth iteration(4) result in a slope that is more positive (i.e., only slightlynegative or close to zero).

The fourth threshold break corresponds to a V_(MIN) higher than theV_(MIN) of the third threshold break, which indicates to the system thatV_(MIN) is still increasing, but at a faster rate than previouslyexpected. Accordingly, values for V_(S) and operating parameters areadjusted for the fifth iteration (5) and may include a smaller V_(S)step 534 and a positive slope 436 that attempts to more closely mirrorthe change or rate of change of V_(MIN). The fifth threshold breakfollowing the fifth iteration (5) can indicate that V_(MIN) has attaineda steady increasing profile similar to the V_(MIN) profile determined atthe fourth threshold break. Therefore, the sixth iteration (6) mayinclude an even smaller V_(S) step 538, compared to V_(S) step 534, anda slope 540 that again is more similar to the V_(MIN) profile, comparedto slope 536. As a general matter, the step size (e.g., for steps 530,534, 538) and the slope (e.g., slopes 532, 536, 540) reflect how wellthe system understands the current profile of V_(MIN) at that time. Ifthe V_(MIN) profile is experiencing a change (e.g., from a steadyprofile to an increasing profile), then the step size may be relativelylarge (e.g., to ensure V_(S) is above V_(MIN)), and the slope may berelatively steep (e.g., a more negative slope). This large step size andsteep slope can help gather an additional data point corresponding tothe V_(MIN) profile relatively quickly. Alternatively, if the V_(MIN)profile is not experiencing a change or rate of change in profile (e.g.,V_(MIN) is increasing at a steady rate), then the step size may berelatively small because the system can better predict the currentprofile of V_(MIN), and the slope may be less steep to more closelyreflect the current profile of V_(MIN).

The sixth iteration (6) also includes a portion 542 wherein the slope ofV_(S) changes from positive to negative. This change may be initiated ifand when a threshold break has not occurred within a given time. Forexample, in some embodiments, in addition to determining new values forV_(S) and operating parameters for a subsequent iteration, the systemmay also determine an elapsed time limit before which the next thresholdbreak should occur. This elapsed time limit may differ for eachiteration. As an example, if the system does not experience a thresholdbreak within an elapsed time limit of, e.g., 35 milliseconds for a giveniteration, V_(S) may be automatically decreased, or decreased at afaster rate, to cause a threshold interruption. The elapsed time limitcan help prevent V_(S) from veering too far away from V_(MIN), andthereby limit unnecessary power loss from the system. The elapsed timelimit can be a preset value manually inputted by an operator orphysician, or can be a determined value that is dynamically adjusteddepending on V_(MIN) and its relationship to V_(S) at that time.

The third portion 504 of the plot 500 corresponds to a decreasingV_(MIN) profile. As shown by the seventh iteration (7), the V_(S) step550 may be larger than the previous V_(S) step 538 because the sixththreshold break occurred after the elapsed time limit was initiated,thereby indicating that the V_(MIN) profile may no longer be increasingat the previously expected rate. As such, the inputted V_(S) for theseventh iteration (7) may be higher than the previous iteration (6) toensure V_(S) remains above V_(MIN) and adequate therapy continues to beprovided to the patient (e.g., a therapy interruption is avoided). Forsimilar reasons, the operating parameters inputted for the seventhiteration (7) may result in a negative slope 552 to ensure a thresholdbreak occurs relatively quickly. Following the threshold break after theseventh iteration (7), the system determines that V_(MIN) is decreasing.In this case, because the previous iteration had a substantiallydifferent profile (i.e., an increasing profile), the system may notconsider one or more of the previous threshold breaks.

The subsequent eighth iteration (8) and ninth iteration (9) can exhibitfeatures similar to those previously described with reference to thefirst portion 502 and second portion 503. For example, values for theV_(S) and operating parameters for the eighth iteration (8) can be basedon the previous threshold breaks, and can result in a V_(S) step 554which is smaller than the V_(S) step 550, and a slope 556 that moreclosely mirrors the V_(MIN) profile, compared to slope 552. Using thesame methodology, the V_(S) step 558 for the ninth iteration (9) issmaller than V_(S) step 554 for the eighth iteration (8), and the slope560 more closely mirrors the V_(MIN) profile, compared to the slope 556.Accordingly, each subsequent iteration can bring V_(S) closer toV_(MIN), thereby decreasing power loss as therapy continues to bedelivered.

From the foregoing, it will be appreciated that specific embodiments ofthe presently disclosed technology have been described herein forpurposes of illustration, but that various modifications may be madewithout deviating from the disclosed technology. For example, someembodiments were described above in the context of adjusting anelectrical signal based on voltage. In some embodiments, othermethodologies may be used, such as adjusting the electrical signal basedon current, impedance, frequency, amplitude or other variable parametersof the electrical signal. As such, other factors for delivering andadjusting the electrical signal parameter can also change depending onthe parameter(s) used. For example, when adjusting the electrical signalbased on impedance, the threshold break may occur when the impedance ofthe electrical signal rises to or above a threshold impedance, insteadof falling to or below a threshold voltage, as is the case for adjustingthe electrical signal based on voltage.

As another example, some embodiments were described above in the contextof particular therapy signals that produce pain relief withoutgenerating paresthesia. In some embodiments, other methodologies may beused to provide pain therapy to the patient, and in some instances, suchmethodologies may provide paresthesia-free pain relief. In someembodiments, techniques generally similar to those described above maybe applied to therapies that are directed to tissues other than thespinal cord. Representative tissues can include peripheral nerve tissueand/or brain tissue.

In some embodiments, similar or identical techniques for handlingcharging and/or discharging processes and parameters may be used in thecontext of therapy parameters that generate paresthesia. Someembodiments were described above in the context of spinal cordstimulators, and in some embodiments, generally similar or identicalcharge parameter selection techniques can be used for implantabledevices that perform functions other than spinal cord stimulation. Insome embodiments discussed above, retrieving, processing and/or otherdata functions are performed at the IPG. In some embodiments, at leastsome of the foregoing processes can be carried out by another componentof the overall system, for example, a non-implantable component. Inparticular, certain processes can be carried out by a charger, based ondata provided by the IPG at the time of charging.

Many of the foregoing processes include determining values, parameters,ranges and/or other quantities. As used herein, “determining” caninclude calculating, extrapolating, interpolating, applying table lookup functions, estimating, and/or other suitable methods. As used herein,“generally” or “approximately,” when preceding a value, should beinterpreted to mean plus or minus 10% of the value, unless otherwiseindicated.

Certain aspects of the technology described in the context of someembodiments may be combined or eliminated in some embodiments. Forexample, in some embodiments, the foregoing techniques can include usingpatient-specific therapy parameters, or battery-specific batteryparameters, or a combination of both. In some embodiments, certain stepsof an overall process can be re-ordered or eliminated.

While advantages associated with some embodiments of the disclosedtechnology have been described in the context of those embodiments,other embodiments may also exhibit such advantages, and not allembodiments need necessarily exhibit such advantages to fall within thescope of the present technology. The examples presented in the followingsection provide further embodiments of the present technology.

To the extent that any of the foregoing patents, published applications,and/or other materials incorporated herein by reference conflict withpresent disclosure, the present disclosure controls.

The subject technology is illustrated, for example, according to variousaspects described below. Various examples of aspects of the subjecttechnology are described as numbered examples (1, 2, 3, etc.) forconvenience. These are provided as examples and do not limit the subjecttechnology. It is noted that any of the dependent examples may becombined in any combination, and placed into a respective independentexample, (e.g., examples 1, 6 or 17). The other examples can bepresented in a similar manner.

Examples

-   -   1. A method for delivering electrical therapy to a patient in a        closed loop manner, the method comprising:        -   delivering, via an implantable pulse generator, a variable            electrical signal having a parameter with a first parameter            value;        -   adjusting the parameter of the electrical signal from the            first parameter value;        -   receiving an indication of a first threshold break,            corresponding to the parameter exceeding or falling below a            first threshold value of the parameter; and        -   in response to the received indication—            -   increasing the parameter by a step size to a second                parameter value; and            -   adjusting the parameter along a determined slope until a                second threshold break occurs.    -   2. The method of example 1 wherein the step size is a first step        size, and wherein the second threshold break occurs at a second        threshold value different than the first threshold value, the        method further comprising:        -   based at least in part on the first and second threshold            values, increasing the parameter by a second step size            different than the first step size.    -   3. The method of example 2 wherein increasing the parameter by        the second step size is based at least in part on a length of        time between the first and second threshold breaks, and wherein        the second step size is less than the first step size.    -   4. The method of example 2 wherein the determined slope is a        first determined slope, the method further comprising:        -   based on at least one of (a) the first and second threshold            values or (b) a length of time between the first and second            threshold breaks, adjusting the parameter along a second            determined slope, different than the first determined slope,            until a third threshold break occurs.    -   5. The method of example 1 wherein:        -   the parameter is a voltage,        -   the first parameter value is a first voltage value, and        -   delivering the electrical signal includes delivering the            electrical signal from a voltage regulator to a current            generating source.    -   6. A method for adjusting an electrical signal associated with        delivering therapy to a patient, the method comprising:        -   delivering, via an implantable pulse generator, an            electrical signal having a parameter with a first parameter            value;        -   adjusting the parameter of the electrical signal from the            first parameter value until a threshold break occurs at a            second parameter value that is equal to or less than a            threshold value; and        -   in response to the threshold break, increasing the second            parameter value to a third parameter value.    -   7. The method of example 6 wherein the parameter corresponds to        a voltage, and wherein adjusting the parameter includes        decreasing the voltage from the first parameter value to the        second parameter value based at least in part on a length of        time between the threshold break and a previous threshold break.    -   8. The method of example 6 wherein the parameter corresponds to        a voltage, and wherein adjusting the parameter includes        increasing the voltage from the first parameter value to the        second parameter value based at least in part on a length of        time between the threshold break and a previous threshold break.    -   9. The method of example 6, further comprising determining a        minimum parameter value below which therapy is not delivered to        the patient, wherein the threshold value is above the minimum        parameter value.    -   10. The method of example 6, further comprising, after        increasing the parameter of the electrical signal to the third        parameter value, adjusting the parameter of the electrical        signal based at least in part on a length of time between the        threshold break and a previous threshold break.    -   11. The method of example 6 wherein the third parameter value is        less than the first parameter value and greater than the second        parameter value.    -   12. The method of example 6 wherein the parameter is a voltage,        and wherein delivering the electrical signal includes delivering        the electrical signal from a voltage regulator to a current        generating source, the method further comprising:        -   converting the voltage provided by the voltage regulator to            a requested current that is delivered to the patient.    -   13. The method of example 6 wherein the threshold break is a        first threshold break occurring at a first point in time, the        method further comprising:        -   delivering, via the implantable pulse generator, the            electrical signal having the third parameter value;        -   adjusting the parameter of the electrical signal from the            third parameter value until a second threshold break occurs            at a fourth parameter value; and        -   in response to the second threshold break, increasing the            parameter of the electrical signal to a fifth parameter            value.    -   14. The method of example 13 wherein increasing the parameter of        the electrical signal to a fifth parameter value is based at        least in part on the first threshold break.    -   15. The method of example 13 wherein adjusting the parameter        from the third parameter value is based at least in part on a        length of time between the first and second threshold breaks.    -   16. The method of example 13 wherein:        -   delivering the electrical signal and adjusting the parameter            of the electrical signal from the first parameter value            comprise a first iteration of a closed-feedback loop,        -   increasing the parameter of the electrical signal to the            third parameter value, delivering the electrical signal at            the third parameter value, and adjusting the electrical            signal from the third parameter value, comprise a second            iteration of a feedback loop, subsequent to the first            iteration, and        -   increasing the parameter to the fifth parameter value            comprises a third iteration of the feedback loop, subsequent            to the second iteration.    -   17. An implantable device configured to deliver therapy to a        patient, the device comprising:    -   a battery;    -   a voltage regulator coupled to the battery and configured to        produce a supply voltage;    -   a current-generating circuit configured to supply a current to        the device based at least in part on the supply voltage; and    -   a computer-readable medium having instructions that, when        executed, cause the device to—        -   deliver the supply voltage, having a first value, from the            voltage regulator to the current-generating circuit;        -   adjust the supply voltage from the first value until a            threshold break occurs, the threshold break corresponding to            a second value of the supply voltage at or below a threshold            value; and        -   in response to the threshold break, increase the supply            voltage from the second value to a third value.    -   18. The device of example 17 wherein:        -   the current supplied to the device is a requested current            from the device,        -   the threshold value is above a minimum voltage value below            which the current generating source is prevented from            supplying the requested current to the device, and        -   the computer-readable medium is configured to control a            difference between values of the minimum voltage and the            supply voltage.    -   19. The device of example 17 wherein:        -   the threshold break is a first threshold break occurring at            a first period in time,        -   the operations of delivering the variable supply voltage and            adjusting the supply voltage comprise a first iteration, and        -   the instructions further cause the device to:            -   deliver the supply voltage at the third value, from the                voltage regulator to the current-generating circuit;            -   adjust the supply voltage from the third value until a                second threshold break occurs, the second threshold                break corresponding to a fourth value of the supply                voltage at or below a threshold value at a second period                in time after the first period in time; and            -   based at least in part on the second threshold break,                increase the supply voltage from the fourth value to a                fifth value.    -   20. The method of example 19 wherein:        -   adjusting the supply voltage from the third value includes            adjusting the supply voltage from the third value based at            least in part on a length of time between the first and            second threshold breaks; and        -   increasing the supply voltage to the fifth value is further            based at least in part on the second value.

1. A method for delivering electrical therapy to a patient in a closedloop manner, the method comprising: delivering, via an implantable pulsegenerator, a variable electrical signal having a parameter with a firstparameter value; adjusting the parameter of the electrical signal fromthe first parameter value; receiving an indication of a first thresholdbreak, corresponding to the parameter being equal to or falling below afirst threshold value of the parameter; and in response to the receivedindication— increasing the parameter by a step size to a secondparameter value; and adjusting the parameter along a determined slopeuntil a second threshold break occurs.
 2. The method of claim 1 whereinthe step size is a first step size, and wherein the second thresholdbreak occurs at a second threshold value different than the firstthreshold value, the method further comprising: based at least in parton the first and second threshold values, increasing the parameter by asecond step size different than the first step size.
 3. The method ofclaim 2 wherein increasing the parameter by the second step size isbased at least in part on a length of time between the first and secondthreshold breaks, and wherein the second step size is less than thefirst step size.
 4. The method of claim 2 wherein the determined slopeis a first determined slope, the method further comprising: based on atleast one of (a) the first and second threshold values or (b) a lengthof time between the first and second threshold breaks, adjusting theparameter along a second determined slope, different than the firstdetermined slope, until a third threshold break occurs.
 5. The method ofclaim 1 wherein: the parameter is a voltage, the first parameter valueis a first voltage value, and delivering the electrical signal includesdelivering the electrical signal from a voltage regulator to a currentgenerating source. 6-20. (canceled)
 21. The method of claim 1 whereinreceiving the indication of the first threshold break includes receivingthe indication of the first threshold break at a first threshold valuegreater than a minimum parameter value below which therapy is notdelivered to the patient.
 22. The method of claim 21 wherein the firstthreshold value and the second threshold value are greater than theminimum parameter value.
 23. The method of claim 1 wherein the parametercorresponds to a voltage, and wherein increasing the parameter includesincreasing the voltage based at least in part on a length of timebetween the first threshold break and a previous threshold break. 24.The method of claim 1 wherein the second threshold break occurs at asecond threshold value greater than the first threshold value.
 25. Themethod of claim 1 wherein the second threshold break occurs at a secondthreshold value less than the first threshold value.
 26. The method ofclaim 1 wherein the step size is based at least in part on a differencebetween the first threshold value and a prior threshold value associatedwith a prior threshold break.
 27. The method of claim 1 wherein, whenthe first threshold value is less than or equal to a prior thresholdvalue associated with a prior threshold break, increasing the parameterby a step size includes increasing the parameter to a second parametervalue less than the first parameter value.
 28. The method of claim 1wherein, when the first threshold value is greater than a priorthreshold value associated with a prior threshold break, increasing theparameter by a step size includes increasing the parameter to a secondparameter value greater than the first parameter value.
 29. The methodof claim 1 wherein adjusting the parameter includes increasing theparameter.
 30. The method of claim 1 wherein adjusting the parameterincludes decreasing the parameter.
 31. The method of claim 1 whereinadjusting the parameter includes— adjusting the parameter at a firstrate, and after an elapsed time limit but before receiving theindication of the first threshold break, adjusting the parameter at asecond rate greater than the first rate.
 32. The method of claim 31wherein the elapsed time limit is 35 milliseconds.
 33. A method fordelivering electrical therapy to a patient in a closed loop manner, themethod comprising: programming an implantable pulse generator to—deliver a variable electrical signal having a parameter with a firstparameter value; adjust the parameter of the electrical signal from thefirst parameter value; receive an indication of a first threshold break,corresponding to the parameter being equal to or falling below a firstthreshold value of the parameter; and in response to the receivedindication— increase the parameter by a step size to a second parametervalue; and adjust the parameter along a determined slope until a secondthreshold break occurs.
 34. The method of claim 33 wherein programmingthe implantable pulse generator to receive the indication of the firstthreshold break includes programming the implantable pulse generator toreceive the indication of the first threshold break at a first thresholdvalue that is greater than a minimum parameter value below which therapyis not delivered to the patient.
 35. The method of claim 33 whereinprogramming the implantable pulse generator to increase the parameter bya step size includes programming the implantable pulse generator to—increase the parameter to a second parameter value less than the firstparameter value when the first threshold value is less than or equal toa prior threshold value associated with a prior threshold break, and/orincreasing the parameter to a second parameter value greater than thefirst parameter value when the first threshold value is greater than aprior threshold value associated with a prior threshold break.